The objectives of this project are to examine cancer incidence and mortality among populations exposed to ionizing and non-ionizing radiation; to characterize the risk of radiation-induced cancer in terms of tissues at risk, dose response, radiation quality, temporal distribution of dose, time since exposure, age at exposure and at observation, and possible modifying influences of other environmental and host factors; and in particular, to quantify excess cancer risk at low dose levels. Groups studied include the Japanese A-bomb survivors, several large populations with documented therapeutic, diagnostic, and occupational exposures to ionizing radiation, and resident populations of SEER reporting areas with different ambient levels of solar UV radiation. Other biological effects, such as chromosomal abnormalities in circulating lymphocytes, are studied for possible insights into radiation carcinogenesis. Close liaison is maintained with experimental scienists concerned with radiation carcinogenesis. Project members serve on committees and task forces advising the government as well as national and international agencies.